The present disclosure relates to semiconductor laser apparatuses, and more particularly, to semiconductor laser devices for which a reduction in chip area is required.
In recent years, semiconductor laser devices are used as a light source for most optical pickups which are used in optical recording apparatuses, optical reading apparatuses and the like for recording media, such as optical disks, magneto-optical recording disks and the like. Their applications cover a variety of products, such as recorders, PCs, cars and the like. The optical disk market is expanding steadily. In particular, recently, the market for the next-generation DVD (Blu-ray), which requires gallium nitride-based semiconductor (AlGaInN) laser devices which employ a blue-violet light emission wavelength, has rapidly spread and is becoming pervasive. Under such a circumstance, a reduction in cost of a blue-violet laser as the light source is crucial in accelerating the penetration of the next-generation DVD.
The cost reduction may be achieved by, for example, reducing a size (chip area) of a laser chip. For example, when a laser chip has a length of 1000 μm and a width of 300 μm, then if the width of the laser chip can be reduced by half (length: 1000 μm, width: 150 μm), the number of laser chips per wafer can be doubled, which significantly contributes to a reduction in manufacturing cost of the laser chip.
The reduction in laser chip area can reduce the cost, but is not limitless.
In laser chips, a stripe-like ridge for injecting a current is typically provided at a center in a transverse direction of the chip (see, for example, Japanese Patent Laid-Open Publication No. 2007-329487).
FIG. 8 is a cross-sectional view of a conventional semiconductor laser apparatus. As shown in FIG. 8, a ridge 605 is provided at a center of a laser chip 601. If the chip has a width of 200 μm, a distance X between the ridge 605 and each edge of the laser chip 601 is 100 μm. A current blocking layer 602 for confining a current is formed on the laser chip 601 on opposite sides of the ridge 605. Moreover, a positive electrode 603 is formed on the current blocking layer 602. On the other hand, a negative electrode 604 is formed on a lower surface of the laser chip 601. Moreover, a wire 606 for supplying a current is coupled to the positive electrode 603. The wire 606 can be disposed, avoiding the ridge 605 so that the bonding damage of the ridge 605 which serves as a path for supplying a current is reduced.
Incidentally, if the width of the chip of FIG. 8 is reduced to, for example, 150 μm, the ridge is disposed at a position of X=75 μm. Here, it is assumed that the wire has a diameter of 50±5 μm, overall variations during fabrication of a laser chip including the accuracy of positioning of a mask and the like (device fabrication process variations) fall within ±5 μm, overall variations during separation of a wafer into chips including the deviation of a cleavage position and the like (separation process variations) fall within ±10 μm, and the positional accuracy of wire bonding is ±10 μm. In this case, a tolerance (margin) of ±30 μm needs to be ensured at a position where the wire is provided. Therefore, the region where the wire is to be disposed needs to have a width of 50±30 μm for each chip, and therefore, if X=75 μm, there is a risk that the ridge will be damaged by wire bonding. The damaged ridge would lead to a reduction in light emission efficiency, resulting in a reduction in yield, a lack of long-term reliability, or the like.
Therefore, when the chip area is reduced, it is necessary to offset the ridge from the center of the chip to provide a structure which allows at least one of regions on the left and right sides of the ridge to provide a sufficient area for wire bonding so as to ensure a sufficient tolerance of the position of wire bonding. In other words, an asymmetric structure is required in which the regions on the left and right sides of the ridge have different widths.